feat: implement blog section with first article

Add blog functionality to the Hugo site:
- Create blog content structure (content/blog/)
- Add blog list and single templates (layouts/blog/)
- Add blog navigation to menu
- Publish first article: "KI Generierte Website - ein Praxisbeispiel"
- Support multilingual structure (German/English)
- Add code block styling for blog posts

The blog section is now accessible at /de/blog/ and /en/blog/
with proper navigation, responsive design, and semantic HTML.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

hugo.toml

@@ -33,11 +33,21 @@ disableKinds = ['taxonomy', 'term']
       description = 'Personal website of Markus Graf'
 
 # Language-specific menus
+[[languages.de.menu.main]]
+  name = 'Blog'
+  url = '/de/blog/'
+  weight = 5
+
 [[languages.de.menu.main]]
   name = 'Lebenslauf'
   url = '/de/cv/'
   weight = 10
 
+[[languages.en.menu.main]]
+  name = 'Blog'
+  url = '/en/blog/'
+  weight = 5
+
 [[languages.en.menu.main]]
   name = 'Curriculum Vitae'
   url = '/en/cv/'